The height of scattering phase center retrieved from InSAR data is considered to be correlated with tree height and the spatial structure of the forest stand. Though some researchers have used simple backscattering models to estimate tree height from the height of scattering center, the effect of forest spatial structure on InSAR data is not well understood yet. A three-dimensional coherent radar backscattering model for forest canopies based on realistic three-dimensional scenes was used to investigate the effect. A fractal tree model (L-system) was used to simulate individual 3-D tree structure of different ages or heights. Trees were positioned in a stand in specific patterns resulting in a 3-D medium of discrete scatterers. The radar coherent backscatter model used the 3-D forest scene as input and simulated the coherent radar backscattering signature. Interferometric SAR images of 3D scenes were simulated and heights of scattering phase centers were estimated from the simulated InSAR data. The effects of tree height, and the spatial distribution patterns of trees on the scattering phase center were analyzed and discussed.